Groundwater radionuclide migration

Buddemeier, R.W. and Hunt, J.R., Transport of colloidal contaminants in groundwater Radionuclide migration at the Nevada Test Site, Appl. Geochem., 3, 535, 1988. 

The reliable long-term safety assessment of a nuclear waste repository requires the quantification of all processes that may affect the isolation of the nuclear waste from the biosphere. The colloid-mediated radionuclide migration is discussed as a possible pathway for radionuclide release. As soon as groundwater has access to the nuclear waste, a complicated interactive network of physical and chemical reactions is initiated, and may lead to (1) radionuclide mobilization (2) radionuclide retardation by surface sorption and co-precipitation reactions and (3) radionuclide immobilization by mineralization reactions, that is, the inclusion of radionuclides into thermodynamically or kinetically stabilized solid host matrices. 

One of the more important factors affecting the isolation of radioactive waste is the rate of release of the radioactivity from the solid waste form to the environment. The most probable mechanism for release and transport of radioactivity from a solid waste form is by leaching of radioactive isotopes with groundwater. The objective of leach-testing various waste forms is to evaluate the rate at which specific hazardous radionuclides migrate from waste if and when the waste form comes in contact with groundwater. In this paper, measurement of leach rates of radioactive waste by a method which incorporates neutron activation is described. 

Geochemical models of sorption and desorption must be developed from this work and incorporated into transport models that predict radionuclide migration. A frequently used, simple sorption (or desorption) model is the empirical distribution coefficient, Kj. This quantity is simply the equilibrium concentration of sorbed radionuclide divided by the equilibrium concentration of radionuclide in solution. Values of Kd can be used to calculate a retardation factor, R, which is used in solute transport equations to predict radionuclide migration in groundwater. The calculations assume instantaneous sorption, a linear sorption isotherm, and single-valued adsorption-desorption isotherms. These assumptions have been shown to be erroneous for solute sorption in several groundwater-soil systems (1-2). A more accurate description of radionuclide sorption is an isothermal equation such as the Freundlich equation ... 

Effects of Groundwater Composition and Eh. Radionuclide sorption on geologic solids is dependent on the chemical composition of the groundwater solution and the redox potential (Eh) of the solid-groundwater system. Aquifers at various depths in the Columbia Plateau formation have -been observed to have significant differences in composition. To accurately model radionuclide migration, it is necessary to understand the effects of chemical components and Eh on sorption and solubility of key radionuclides. An additional benefit of this work is to better understand the mechanisms of sorption and desorption of the radionuclides. 

M. Dozol, R. Hagemann, Radionuclide Migration in Groundwaters Review of the Behaviour of Actinides, Pure Appl. Chem. 65, 1081 (1993)... 

Broyd T. W., Grant M. M., and Cross J. E. (1985) A report on intercomparison studies of computer programs which respectively model (i) Radionuclide migration (ii) Equilibrium chemistry of groundwater. EUR 10231 EN, Commission of the European Communities, Luxembourg. 

The aim of this work was to determine the significance of groundwater colloids in far-field radionuclide migration. 

A similar pattern of radionuclide activity In groundwater was Identified by the RFI/CMS for the 100-NR-l Operable Unit In Its study of radionuclide migration from the 116-N-l crib and trench (DOE-RL 1990). 

Sorption onto rock samples pretreated with simulated ENF groundwater (pH 12.5 at 25°C). The solutions used in the experiments simulate the solution composition measured at the end of the pretreatment process, and have pH in the range 8-10. These experiments simulate the case where radionuclides migrate into the geosphere after development of the ADZ. 

Dozol, M. Hagemann, R. 1993. Radionuclide migration in groundwaters review of the behaviour of actinides. Pure and Applied Chemistry, 65, 1082-1102. 

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